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Hairy senna (Senna hirsuta)

Hairy senna can invade and completely dominate pastures and other disturbed areas in Australia. It can become a major crop weed within two or three seasons, and its seeds can remain viable in soil for up to 10 years.

Key facts

Type: Weed, shrub.

Native to: South America, most likely Brazil.

Established in: QLD.

Other names: Sicklepod, Woolly Senna, Slimpod Glaberrima Senna, Stinking Cassia.

Best time to act: Treat seedlings while they are young, and slash established plants while flowering but before seed set.

Identification

  • It is an upright herb or small shrub, 0.5 to 3 metres tall.
  • The stems, leaves and pods are densely covered with long greyish-white hairs.
  • Each leaf has three to six pairs of large leaflets with pointed tips, and a small finger-like gland on the leaf stalk.
  • Yellow to deep orange-yellow flowers grow in clusters of usually two to eight in the leaf forks.
  • The slender, flattened pods are 10 to 18 centimetres long, usually curve downwards and turn brown as they mature.
  • Look-alike: It resembles Sicklepod, Java Bean, Coffee Senna, Smooth Senna and Arsenic Bush, but hairy senna has long greyish-white hairs covering its stems, leaves and pods.
  • Look-alike: Its pods are flattened and straight to slightly down-curved, unlike the rounded or almost rounded pods of most similar species.

Where it grows

In Australia it occurs in coastal Queensland and northern New South Wales, especially in pastures and rainforests, and has also been recorded in the Northern Territory.

Why it matters

  • It can invade and completely dominate pastures and other disturbed areas.
  • It has the potential to become a major weed of crops within two or three seasons.
  • Infestations can remain a problem for many years because seeds can remain viable in the soil for up to 10 years.

How it spreads

  • It spreads only by seed.
  • Stock may eat the seeds, which can then germinate in dung, and seeds may also be carried by water.
  • Seeds can spread as contaminants of agricultural produce or in mud on animals, people, machinery and vehicles.

Control options

  • Prevention is the best control method; avoid grazing stock in infested paddocks and prevent seed from being moved to clean areas.
  • Slashing can reduce old plants to a manageable size but will not kill them; slash while plants are flowering and before seed set.
  • Rotary hoeing or discing followed immediately by sowing improved pasture can be effective when the grasses are well managed and individual plants are spot sprayed.
  • Use registered herbicides according to current label directions; spraying is most effective on young seedlings and becomes more difficult as plants age.

Hygiene and washdown

  • Clean machinery on site to reduce the risk of spreading seeds.
  • Check vehicles and remove mud before moving from infested areas, as seeds can be carried in mud.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Restricted matter, category 3. Do not give it away, sell or release it into the environment. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Not a priority weed. Not a state or regional priority weed in NSW. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Not listed. Not found in the Western Australian Organism List. Check with DPIRD before moving or keeping it.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Not declared. Not on the NT A to Z weed list, and Weeds Australia does not list it as declared in the NT. Check the NT declared weeds list before moving or planting it.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)

Sources